yup, but thats the answer...thats what the professor said, and i checked it in the text as well, same principle as the airplane wing, that's the one

Here's my take on 2):

Please consider the following:

NOTE:
Both bodies are in a state of free-fall.
Thus, a condition of weightlessness will exist i.e microgravity.

Take a look at the terminal velocity equation.
It's inversely proportional to cross-sectional area and directly proportional to weight. The rest of the variables are constants.

Since, the weightless condition applies, the numerator can be neglected.

The only unknown quantity is cross-sectional area.

Take note here:

Larger objects have lower terminal velocity as compared with smaller objects.

So,

This is the trick in this question. Weight is a misleading quantity in this case.

However, they have mentioned both objects have the SAME SHAPE.

I believe, this signifies identical cross-section.

Thus, both objects will have the SAME terminal velocity.

If we look at the fundemental velocity equation,

v1 = u1 + gt1 (v1 = terminal velocity of A, u1 = init. velocity of A)
v2 = u2 + gt2 (v2 = terminal velocity of B, u2 = init. velocity of B)

Since v1 = v2,

u1 + gt1 = u2 + gt2

Since, the question says both bodies START falling TOGETHER, this would signify they are both initially at rest and start falling at the same instant.

Thus, u1 , u2 = 0

Therefore, t1 = t2.

Thus, they should reach terminal velocity at the same time.

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Last edited by varun on Dec-19-2006 at 10:58

quote:

Originally posted by varun Here's my take on 2): Please consider the following: NOTE: Both bodies are in a state of free-fall. Thus, a condition of weightlessness will exist i.e microgravity. Take a look at the terminal velocity equation. It's inversely proportional to cross-sectional area and directly proportional to weight. The rest of the variables are constants. Since, the weightless condition applies, the numerator can be neglected. The only unknown quantity is cross-sectional area. Take note here: Larger objects have lower terminal velocity as compared with smaller objects. So, This is the trick in this question. Weight is a misleading quantity in this case. However, they have mentioned both objects have the SAME SHAPE. I believe, this signifies identical cross-section. Thus, both objects will have the SAME terminal velocity. If we look at the fundemental velocity equation, v1 = u1 + gt1 (v1 = terminal velocity of A, u1 = init. velocity of A) v2 = u2 + gt2 (v2 = terminal velocity of B, u2 = init. velocity of B) Since v1 = v2, u1 + gt1 = u2 + gt2 Since, the question says both bodies START falling TOGETHER, this would signify they are both initially at rest and start falling at the same instant. Thus, u1 , u2 = 0 Therefore, t1 = t2. Thus, they should reach terminal velocity at the same time.

The terminal velocity equation by definition applies to objects in freefall, hence it needs no tweaking or ignoring of any part of it, numerator or otherwise.

An object in freefall is not weightless. Terminal velocity is the velocity at which upward air resistance is equal to downward force (weight).

Again if ONLY the cross sectional area is relevant, and the weight is completely irrelevant for objects in freefall, as you suggest, then the elephant has a lower terminal velocity than the feather, which it will reach first meaning the feather must hit the ground first.


Isn't it within the ambit of everyone's common experience that when you drop a piece of polystyrene it drops much slower than a piece of metal of the same shape?

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Last edited by astroboy on Dec-20-2006 at 02:18

I'm still wondering how he can talk about an upward lift for an upward rising ball. I could be wrong ofcourse, but that looks really strange.
If the baseball in question is thrown horizontally, like how a pitcher would throw, then it might rise up due to the high pressure on the lower side.

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quote:

Originally posted by Omega_M I'm still wondering how he can talk about an upward lift for an upward rising ball. I could be wrong ofcourse, but that looks really strange. If the baseball in question is thrown horizontally, like how a pitcher would throw, then it might rise up due to the high pressure on the lower side.

Yeah I've been looking up stuff about bernoulli's principle and that answer doesn't make much sense either. If it's a high school physics teacher then I'd be inclined to say s/he is wrong.

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"my son will be a gienues(sp?)" - Originally posted by Googooly
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"also can someone post the link to my mom's forum, thank you!" - Originally posted by miamitrance04
"dude man its not me its what the world does to me. Trust me I'm a normal person people just constantly fuck with me." Originally posted by ********
"I can see Lira getting a hard-on already. And believe me, Brazilian ass rape is the worst." - Originally posted by Meat187